Inverse Marx generator

What would be the point?

You still end up with the same power? Why would you go through all the trouble when you can get 1000x more power from your outlet?

Say you have a 1M van de graff, you get maybe 1uA from it... thats just 1W. No matter how you configure it you'll never get any more power from it.

Your caps are in series which means the voltage across them is 1/n of the total voltage. When you wire them up in parallel your new total voltage is

1/n.

e.g., suppose you have 1M voltage and 1000 caps in series. Your new voltage would then be 1000V and your current would be 1000 times the original.

i.e., your just making a transformer. Any time you have a predetermined amount of energy you can only ideally transform it into a different "form"(since energy can neither be created nor destroyed).

On a sunny day (Sat, 3 Jul 2010 01:15:13 -0500) it happened "Tim Williams" wrote in :

Relays?

Think nuclear battery, or lightning.

parallel. It's like an inverse Marx generator, or a synchronous C-W multiplier. How would you do it?

That's just a charge pump working in the down direction. The switches are the problem.

John

useful. =A0Think nuclear battery, or lightning.

caps in parallel. =A0It's like an inverse Marx generator, or a synchronous= C-W multiplier. =A0How would you do it?

How would you charge caps, without enough current?

very

By having current. See above.

Tim

--=20 Deep Friar: a very philosophical monk. Website:

"John Larkin" wrote in = message news: snipped-for-privacy@4ax.com...

Yup. So we need to make a flying capacitor switcher with >10kV = isolation.

I don't think your favorite 400V optoisolators are up to the task :)

Tim

--=20 Deep Friar: a very philosophical monk. Website:

Not to change the subject (who, me?) you could buy a bunch of 15KV oil caps, charge them up one at a time, and physically stack them in series. Maybe start with the series string lying on the ground and use a pully and some plastic rope to lift the stack up in the air as each one is charged, literally "erecting" a Marx generator. 30 would get you to about half a million volts. Without switches or spark gaps, discharge impedance would be low.

Use two ropes, at the HV and and midpoint. After it's assembled, hold up the midpoint and let the hot end droop down towards ground in an inverted "V" shape.

Or do it horizontally, with the caps in an almost-closed ring, on PVC pipe supports or hanging on plastic ropes from some trees or something. Now just walk around the circle and charge one cap at a time. Carefully.

Or stack the caps and have each one have its own battery-powered flyback charger. Great fun on the 4th of July.

John

useful. =A0Think nuclear battery, or lightning.

It's an exercise in finding utility, then. How about exciting the plate of a vacuum tube? Then, you can feed a 'suitable' frequency into the grid and get whopping AC power output from a transformer on the cathode circuit.

A reverse Van Der Graph Generator ?

A constantly rotating Variable Capacitor with comutator contacts to apply the high voltage at Min Cap and then bleed off the converted charge at Max capacitance?

Q=CV

Perhaps a cascade of them in series?

............... Zim

But they don't make tubes that run 500kV, at least that are meant to do = any AC. Certainly no NOS radio tubes. And low efficiency, and low = bandwidth, and blah, blah.

Tubes in the 10kV range might not be too horrible for doing the = series-parallel conversion (sync rect with tubes?), but driving the = heaters is a pain. Even big stacks of FETs are appealing at that rate. = And even then, you might as well go with 500 or 1000V caps, and more = stages, so you get a single transistor per stage without cascoding.

So the question remains, how does one change HV into useful V? Flying = capacitors, sure, but can you tackle the isolation?

Tim

--=20 Deep Friar: a very philosophical monk. Website:

Certainly no NOS radio tubes. And low efficiency, and low bandwidth, and blah, blah.

conversion (sync rect with tubes?), but driving the heaters is a pain. Even big stacks of FETs are appealing at that rate. And even then, you might as well go with 500 or 1000V caps, and more stages, so you get a single transistor per stage without cascoding.

capacitors, sure, but can you tackle the isolation?

Carefully aimed pointed wires? :o) Gently drifting the ion flow,

Step-down Van der Graaf upthread sounds good?

Grant.

snipped-for-privacy@q12g2000yqj.googlegroups.com...

ny AC. =A0Certainly no NOS radio tubes. =A0And low efficiency, and low band= width, and blah, blah.

OK, so use a klystron (those DO scale to 500 kV) but your AC output will be at a possibly inconvenient frequency. 'low efficiency' is not as big an issue as you might think; there are

23MW klystrons, at that scale (or even at 0.5 kW in a microwave oven) the efficiency beats out all solid state competitors.

Hmm, at that voltage, heater power is inconsequential, and if it runs at = a lazy 500MHz let's say, there are plenty of schottkies around that = could convert it, maybe not at great efficiency, but it's something. = They don't have 500kV klystrons at AES though. :) It's one possible = solution, if one were to make a startup, and cook their own tubes, and = "harness" lightning.

Tim

--=20 Deep Friar: a very philosophical monk. Website:

"Tim Williams" schreef in bericht news:iAAXn.3984$ snipped-for-privacy@newsfe11.iad... Let's say you had a really high voltage, low current source. Not very useful. Think nuclear battery, or lightning.

So let's say you use it to charge a stack of caps. Then you rewire the caps in parallel. It's like an inverse Marx generator, or a synchronous C-W multiplier. How would you do it?

Tim

-- Deep Friar: a very philosophical monk. Website:

By far most of the high voltage sources I know about you need a lot more energy to operate them then you ever can retrieve. Todays nuclear batteries as used in some spacecraft are low voltage. Only lightning consists of very high voltages and currents but they are very, very short so the total energy of a lightning strike is some Ah only. So harvesting this energy is likely to use more then it yields.

petrus bitbyter

I think there are different designs: one uses beta emitters and generates a kilovolt or so, one uses thermal conversion (with thermopiles) off an isotope heat source and generates low V.

x

I think they call that a "Railgun".

But E=QV, hence, if charge is to be conserved, the system will have to give up energy somewhere as the voltage is reduced. In practice, the rotating mechanism would absorb that energy.

Capacitors switched from series to parallel will conserve both charge and energy.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

Then it follows that E = C * V^2

which of course it doesn't.

John

Quite right, put it down to haste.

E=QV/2

It still implies that reducing V by increasing C involves a loss of energy.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)